well it sounds like I'm not the only one that has had this problem. and 2 of the 3 gauges I have are liquid filled. and from my understanding the liquid is only to keep the needle steady. my non filled one is steady as the liquid filled ones. and Hammertime you may have something there with the heat. mine changed bad after the engine heated up and I made a run. is there any way of testing them to see if they are correct.
Andy